Methods

Pathways leading to increased ceramide concentrations in inflamed versus non-inflamed
adipose tissue were investigated by quantifying expression levels of key enzymes involved
in ceramide metabolism. Sphingomyelinases (sphingomyelin phosphodiesterases SMPD1-3)
were investigated further using immunohistochemistry to establish their location within
adipose tissue, and their mRNA expression levels were determined in subcutaneous and
intra-abdominal adipose tissue from both non-obese and obese subject.

Results

Gene expression levels of sphingomyelinases, enzymes that hydrolyse sphingomyelin
to ceramide, rather than enzymes involved in de novo ceramide synthesis, were higher in inflamed compared to non-inflamed adipose tissue
of obese women (with high and normal liver fat contents respectively). Sphingomyelinases
were localised to both macrophages and adipocytes, but also to blood vessels and to
extracellular regions surrounding vessels within adipose tissue. Expression levels
of SMPD3 mRNA correlated significantly with concentrations of different ceramides
and sphingomyelins. In both non-obese and obese subjects SMPD3 mRNA levels were higher
in the more inflamed intra-abdominal compared to the subcutaneous adipose tissue depot.

Conclusions

Generation of ceramides within adipose tissue as a result of sphingomyelinase action
may contribute to inflammation in human adipose tissue.